Novartis disclosed early clinical data indicating its investigational actinium-225 radiopharmaceutical produced measurable anti-tumour activity in prostate cancer patients, including individuals who had previously received Pluvicto. The interim results come from a 101-patient trial presented at the American Society of Clinical Oncology meeting in Chicago.
Among patients in the study who had been treated earlier with Pluvicto, 52.5% experienced a decline in prostate-specific antigen - or PSA - levels of at least 50% while on the actinium-based therapy. Elevated PSA is commonly used as a marker for prostate cancer activity.
Response rates were higher in cohorts without prior Pluvicto exposure. More than 85% of patients with no prior treatment registered PSA reductions of at least half, and 58.8% of patients who had received chemotherapy first saw PSA levels decline by 50% or more, according to the data presented.
Industry analysts at TD Cowen characterized the preliminary efficacy signal as clear, but they urged caution because the therapy has been associated with substantial side effects. The analysts highlighted high rates of dry mouth and cases of severe anemia as adverse events that will need careful management as development proceeds.
Novartis Chief Medical Officer Shreeram Aradhye noted that larger clinical trials will be required to more fully determine the severity and reversibility of the adverse effects observed, particularly if the radiopharmaceutical is used earlier in treatment sequences where tolerability expectations differ.
The Swiss drugmaker has been expanding its investment in radioligand therapies - agents that couple a radioactive isotope to a molecule designed to target cancer cells directly - and is advancing two late-stage studies of the experimental actinium compound. Aradhye said that radioligand therapies now account for nearly 40% of Novartis' cancer R&D investments.
Novartis already markets the approved radiopharmaceuticals Pluvicto and Lutathera, which together generated $2.8 billion in revenue last year. The experimental molecule differs from Pluvicto in its radioactive payload: Pluvicto employs lutetium-177, a beta-emitting isotope, while the investigational therapy uses actinium-225, an alpha emitter. On the difference between the isotopes, Aradhye said: "The difference is that much higher amounts of energy (are) delivered across a much smaller distance, and the potential for greater efficacy."
Some analysts have warned that current global supply of actinium-225 may be insufficient to meet rising clinical demand, though the article's sources noted that new production efforts could ease such constraints. Novartis has said it is planning around future isotope needs and, in February, entered into a long-term supply agreement for actinium with U.S.-based medical isotope producer Niowave.
As Novartis moves the actinium program forward into late-stage testing, the combination of encouraging early efficacy signals and notable safety and supply considerations will shape how regulators, clinicians and investors evaluate the therapy's potential role in prostate cancer treatment.